Composite apex seal

ABSTRACT

An apex seal construction in a rotary internal combustion engine is disclosed as well as a method of making same. The apex seal is carried within a slot of the rotor and is urged by gas pressure for maintaining sealing contact between a side of said slot and the rotor housing. The apex seal has a supporting body formed of a light weight metallic material, such as aluminum, and a wearresistant coating applied by plasma jet as a substantial envelope thereabout, the combined heat of the plasma as well as the force of impact of the jet combine to provide an improved adherency between the coating and light weight body. Immediately subsequent to plasma jet deposition, the coated apex seal is subjected to a quenching medium to develop a hardness of at least 40 Rc, uniformly throughout the bulk of the material the coating having a controlled porosity of 2-5% and a thickness in the range of 1525 mils.

United States Patent Telang Oct. 7, 1975 COMPOSITE APEX SEAL [21] Appl.No.: 390,133

Primary Examiner--C. .l. l-Iusar Assistant Examiner0. T. SessionsAttorney, Agent, or FirmJoseph W. Malleck; Keith L. Zerschling [5 7]ABSTRACT An apex seal construction in a rotary internal combustionengine is disclosed as well as a method of making same. The apex seal iscarried within a slot of the rotor and is urged by gas pressure formaintaining sealing contact between a side of said slot and the rotorhousing. The apex seal has a supporting body formed of a light weightmetallic material, such as aluminum, and a wear-resistant coatingapplied by plasma jet as a substantial envelope thereabout, the combinedheat of the plasma as well as the force of impact of the jet combine toprovide an improved adherency between the coating and light weight body.Immediately subsequent to plasma jet deposition, the coated apex seal issubjected to a quenching medium to develop a hardness of at least 40 Runiformly throughout the bulk of the material the coating having acontrolled porosity of 25% and a thickness in the range of 15-25 mils.

4 Claims, 6 Drawing Figures U.S. Patent 0a. 7,1975 Sheet 1 of2 3,910,734

FIG.3 22 PIC-3.4

COMPOSITE APEX SEAL BACKGROUND OF THE INVENTION Chatter marks areconsistently experienced on the inner wall of the rotor housing for arotary engine constructed according to prior art knowledge. At higherspeeds of rotation of the piston, this is particularly notable andeventually result in an ineffective sealing between the rotor and therotor housing because the sealing strips are unable to conform to theconvolutions of such chatter marks. The chatter marks result in partfrom unusually high dynamic loading at certain zones of the epitrochoidpath. The rotor, being eccentrically mounted, imparts inertial energy tothe seal element to move not only radially outwardly but transversely ina slot of the rotor housing. Gas pressure promotes a force to cause thesealing strip to engage a side of the slot as well as engage the rotorhousing surface. As the dynamic loading is accentuated in certain zones,chatter marks appear as a result of gouging of the surface of the rotorhousing.

There is a high rate of abrasion between the inner epitrochoid surfaceof the rotor housing and apex seals on the rotor. To overcome this,abrasion resistant coatings or layers have been applied to the apexseals. Difficulties are encountered in formulating the abrasionresistant material since it must withstand the high operatingtemperature conditions in the engine and there must be an economical,efficient process for applying the coating. Most importantly, when theengine is in operation, the abrasion resistant layer can easily separatefrom its substrate, breaking away due to insufficient bond.

One possible way known to the prior art of increasing the abrasionresistance of the seal is to electrolytically apply a layer of nickelcontaining embedded particles of silicon carbide. However, electrolyticdeposition results in uneven coating thickness due to the sharply turnedconfiguration of the crown of an apex seal. The prior art has also usedceramic materials applied particularly by a flame spray technique. But aceramic layer applied by flame spraying is brittle and has a lowcoefficient of thermal expansion resulting in thermal stresses duringoperation of the engine. Attempts to improve the adhesion between flamesprayed materials has comprised (a) undercutting slots, (b) usingintermediate layers to promote a metallurgical bond therebetween, bothof which is expensive and time consuming and has not resulted in optimumadhesion.

SUMMARY OF THE INVENTION A primary object of this invention is toprovide an improved apex seal construction for use on the rotor of arotary internal combustion engine.

Another object of the invention is to provide a composite apex sealconstruction that has unprecedented adherence between a wear-resistantcoating and the supporting substrate.

Other objects of the invention include provision of a wear-resistantcoating as part of the composite apex construction as in the foregoingobjects, the wear resistant coating having limited porosity resultingfrom the uniqueness of deposition and the wear-resistant portion havinga higher level of hardness at elevated temperatures than relatedcoatings of the prior art. The composite apex seal construction ischaracterized by a very low modulus of the elasticity therebycooperating to subject the wear-resistant coating to less stress duringengine operation.

Yet still another object of the invention is to provide a unique methodfor fabricating a composite seal construction, the method comprising:(a) Defining a metallic supporting portion for an apex seal particularlycomprised of an alloy of aluminum or a denser material hollowed forweight reduction; (b) Subjecting the supporting portion to a plasmaspray of admixed powders consisting preferably of martensitic stainlesssteel and nickel-based alloy powders, each of generally the samehardness; (The powders are introduced to a plasma gun having a divergingsupersonic type nozzle, the powders are subjected to a temperature of atleast 2800F and impelled by the force of the plasma jet to deform in anirregular manner with less porosity than experienced by the prior art).(c) Immediately upon deposition of said plasma impelled powder, the bodyand coating are subjected to a quenching medium effective to develop ahardness level of at least R 80. The force of the plasma jet results ina mechanical bond between the coating and supporting portion which is atleast 8,500 psi. as determined by an epoxy adhesion test.

SUMMARY OF THE DRAWINGS FIG. 1 is an elevational view of a rotaryinternal combustion enginehaving a portion broken away to illus tratethe orientation of the side housings relative to the rotor housings andagainst which the apex seal construction must operate;

FIG. 2 is a sectional view taken substantially along line 2--2 of FIG.1;

FIG. 3 is an enlarged central sectional view of an apex sealconstruction embodying the principles of this invention;

FIG. 4 is a broken side-elevational view of the construction shown inFIG. 3;

FIG. 5 is a schematic illustration of the microstructure of the coatingsystem of the apex seal construction;

FIG. 6 is a schematic layout diagram of a plasma spraying apparatusillustrating the method of depositing the coating system of thisinvention.

DETAILED DESCRIPTION Turning now to FIGS. 1 and 2, the inventionpertains to an apex seal construction 10 which is of the type adapted tofit within slots 11 defined within the apices of a rotor mounted forplanetary movement within an epitrochoidally shaped housing chamber 12.The apex seal construction serves to separate the space between thetriangulated rotor 12 and. the surrounding housing walls into threevariable volume chambers a, b and c. To experience a four-cycle engineoperation in each of the variable volume chambers, during a singlerevolution of the rotor, the efficiency of the apex seal constructionbecomes critical.

The structure defining the epitrochoidally shaped chamber 13 iscomprised of side housings 14 and 15, spaced apart a distance slightlylarger than the width of the narrow rotor. The side walls are connectedby a rotor housing 16 at the outer extremity which carries an internallyfacing epitrochoidally shaped wall 16a. Each of the side housings areprovided with a wearresistant coating system 17, the coating extendingthroughout the entire area of the side walls which do come in contactwith the ends of the apex seal construction during operation. The rotorhousing has a coating system effective to resist wear from engagementwith the apex seal construction. Each of these coatings on the housingportions may be comprised of materials such as electrolyticallydeposited nickel with embedded silicon carbide particles. The coatingsystem should have a minimum hardness level of at least 30 R to workcompatibly with the metallurgical properties of the apex sealconstruction disclosed herein.

The apex seal of this invention particularly comprises a supportingportion which is defined as an elongated strip effective to span thewidth of the combustion chamber for providing a continuous sliding sealengagement between the epitrochoid wall of the rotor housing and a sideof a slot extending across an apex of the rotor. As shows in FIG. 4, theelongated supporting portion 20 may have an undercut portion 21 definingfeet 22 and 23 at the opposite ends of the elongation portions of thefeed fitting within corner seals 24 which are effective to promote aproper seal at the juncture between side seals 25 and the apex seals.The undercut portions facilitate shift of gas pressure forces operatingupon the underside of the apex seal to move the seal to one or the otherside of the slot for affecting the appropriate seal at different zonesof the epitrochoid path.

The supporting 20 is preferably constituted of a cast material such asaluminum having a specific gravity of about 2.6 and a modulus ofelasticity of about 11-12 million p.s.i. It is important that theselected material for defining the supporting portion, be of lightweight, be resistant to the environmental conditions of temperature andcorrosion experienced within a rotary engine, and have a low modulus ofelasticity so that there will be more flexing of the coatingsuperimposed on this supporting portion (the more rigid supportingportion will result in higher stresses on the coating to provide asurface contact as opposed to a line contact). A particularly desirablealuminum for this purpose is type 2,618 or K01 which has high elevatedtemperature strength properties. It contains an analysis of copper,0.62% silver, 0.29% titanium, and the balance aluminum. The aluminumalloy is subjected to solution heat treatment conditions for 16 hours at995F and quenched in cold water to 60F, then heated to 3l0370F for 5-2Ohours.

The as-cast surface of the supporting portion is relatively rough whichfacilitates bonding to the coating applied thereover. Other material maybe selected for the supporting portion, such as steel, which has beenhollowed to reduce the average weight throughout the volume normallyenclosed by the supporting portion. In any event the materials shouldhave a specific gravity for purposes of the full volume of itsconfiguration of no greater than 3.0 and have a modulus of elasticity noless than 12 million p.s.i.

A wear-resistant coating 27 is applied to the supporting portion and isadapted to substantially envelope the supporting portion leaving onlythe bottom surface 28 exposed. The coating is a plasma sprayed admixtureof metal bonded refractory powders and should have a low content of drylubricants. Preferably an admixture of martensitic stainless steel andnickel-based alloy powders can be used, both being of generally equalhardness. Another is iron and titanium carbide. The critical importanceis the use of the plasma spray technique according to the parametersherein. The admixed powders which form the chemicalanalysis of thecoating, should be subjected to a temperature of at least 2,800F andsubjected to a jet velocity which approaches sonic and in someembodiments is supersonic, such as Mach II. The adhesive bond resultingfrom the combination of temperature and jet velocity promote an adhesionfor metal bonded refractories which will be at least 8,500 psi. asdetermined by an epoxy adhesion test. Such a test requires that apredetermined area of the coating be coated with an epoxy joint, thejoint is coupled to a mechanical device for applying stress. The epoxybond itself has an adhesion greater than the expected bond between thecoating and substrate. Prior art coatings carried out according to otherspray techniques have a typically maximum adhesion quality of about4,0005,5OO p.s.i. as determined again by the epoxy adhesion test.

Equally important, is the denser coating that results from using thetechnique herein. By virtue of the increased velocity of the jet streamcarrying the heated particles, the particles impact with considerablygreater force resulting in distortion of the particles and greaterelimination of voids that may occur in normally sprayed coatings.Instead of the typical 6l5% porosity that may occur in normal sprayedcoatings, the density herein is uniformly in the range of 25% which iscritically important to control oil permeation in the coating. More than5% porosity will lead to excess flooding and interference of sealingefficiency of the apex seal.

To obtain the combined virtues of high wearresistance, strong adhesionand a denser coating, certain parameters must be observed. For example,the particle size of the admixed metal and refractories powders shouldbe in the range of 44-74 microns, this being a relatively fine powder.An improved surface finish is produced and has a surface finish in therange of 400 r.m.s. Subsequent polishing to obtain a 4-8 r.m.s. finishsurface is facilitated. Additionally, the density is improved as aresult of controlled particle size and can reach -98% theoreticaldensity. The deposition rate of the powders should be at least 10 lbs.per hour thereby increasing the efficiency of the deposition technique;the increased deposition rate results from the higher jet velocity andincreased temperature. The

selected temperature of the plasma jet should be arranged so that theparticles are substantially heated to solution conditions therebyallowing for a phase transformation in passing through the plasma gun.This permits increased hardness when the coating is quenched immediatelyafter deposition. One metal bonded refractory composition; spray coatedaccording to this invention appears in FIG. 5; martensitic stainlesssteel and nickel-based alloy were selected as the admixed powders. Somemartensitic stainless steel particles, instead of having a perfectlyglobular shape, assume a striated configuration; the nickel-based alloy,being somewhat larger in particle shape, assumes a highly irregularconfiguration. Both configurations combine to provide a good binding andinter-locking between the particles of the coating. The voids (whichconstitute porosity) in the coating are substantially less. The roughas-cast aluminum substrate is somewhat heated by the impacting particlesto provide a limited degree of alloying between certain of the adjacentparticles. This is a self-contained heat treatment as a result of thisinvention which produces a lower oxygen content in the coating.

Method A particularly useful method of applying the coating of thisinvention is to provide forat least sonic and preferably supersonicplasma spray. A Mach II stream may be used to obtain particle velocitieswhich are considerably higher resulting in increased coating density andbond strength. The higher density results because of the associatedhigher kinetic energy of the particles. The bond strength of the coatingalso is increased due to the increased mechanical energy expenditure atimpact resulting in distortion and interlocking of the particles. Theplasma jet velocity is increased by the use of an exit throat insertwhich has a straight bore and a diverging section. As in conventionalchemical spray methods, the principle of the plasma process is thatenergy, both thermal and kinetic, is imparted to the injected particlesby the plasma stream. Since this energy transfer is basicallycollisional, both the temperature and velocity of any entrained particleare relative to but lower than the properties of the plasma stream. Inorder to obtain a near molten state and an optimum exit velocity of theinjected particles, not only the physical properties and parameters ofthe plasma stream, but also those of the injected particulates have tobe considered.

In subsonic plasma spray systems, the temperature and density of theplasma stream are generally varied to maintain the required temperaturelevel 'of an injected spray powder. This is accomplished by eitherindependent or simultaneous adjustment of arc powder and arc gas flow.As the ambient pressure is fixed at one atmosphere, this adjustmentresults in either increasing or decreasing the plasma stream exitvelocity due to the pressure variations upstream of the exit throat. Butif the maximum arc chamber pressure is redesigned so as to operateconsiderably above three atmospheres (29.4 p.s.i.) and if the arc gas orgas mixture is redesigned so as to have an increased enthalpy abot 1,000b.t.u./lb., and if the exit throat has not only a straight section butalso a diverging section, the exit velocity of the plasma jet can beincreased to supersonic conditions. As an example, to obtain supersonicMach II exit conditions at one atmosphere of ambient pressure, an arcchamber pressure of 6.5 to 8 atmospheres (81 to 103 p.s.i.g.) and anargon plasma stream with an enthalpy ranging from 1,500 to 4,000b.t.u./lb. in required. The nozzle throat to exit area ratio is matchedto the required pressure ratio for these conditions. This prevents flowshock formation and creates a fully expanded plasma stream closely sizedto the exit diameter of the nozzle. Therefore, the heated andaccelerated particles remain confined within the stream from the nozzleexit to the workpiece. Arc power levels of at least 80 kw must beutilized to obtain the arc gas pressure conditions required.

Turning now to FIG. 6, a typical schematic arrangement of an apparatusfor the described method is shown. The plasma gun contains a gas arcchamber 31 having an exit throat which particularly has a straight boresection 33 and a diverging section 34. The gassupply is introduced atthe left hand portion of the gas chamber 31 and an arc is created acrossthe chamber by virtue of an arc power supply 36. The metallic andrefractory powders are introduced to the gun from a power feeder 37 andcarried to a preheating tube 38 which is powered by a powder preheatsupply 39; the powder is then conveyed to a precise location in the exitthroat by way of passage 40 which is slightly angled (at 4lwithreferenceto a center-line 42 of the passage) and enters the exit throatprecisely at the juncture of the straight bore se'c'tiorranddivergingsection, The stream from the plasmagun is directed at an apexseal supporting portion 45 which is carried on a movable support 46. Theentire workpiece, as well as the plasma jet, is enclosed within achamber 44 evacuated by way of appropriate mechanical equipment 47. TheWorkpiece is maintained at a specific electrical potential by way of atransferred are power supply 48 so as to receive plasma spray particles.

I claim as my invention:

1. An apex seal for a rotary internal combustion engine and havingsurfaces to be sealed, comprising:

a. a supporting portion defined to extend between said surfaces and iscomprised of a metal consisting essentially of aluminum and having aspecific gravity no greater than 3.0 and. a modulus of elasticity noless than 12 million p.s.i.,

b. a wear-resistant coating substantially enveloping said supportingportion and having a thickness between 0.0l5 inches and 0.025 inches,said coating being comprised of an admixture of two different types ofabrasion resistant particles having a particle size no greater than 74-microns, said particles being self-fused to each other providing limitedporosity of 25%, said coating being mechanically locked to saidsupporting portion with a uniform adhesive force no less than 8,500p.s.i. as determined by an epoxy test procedure, said adhesive forceresulting from the impaction of said abrasion resistant particlesagainst said supporting portion by a plasma jet having a flow velocityin excess of Mach I.

2. An apex seal as in claim 1, in which the hardness of saidas-deposited coating is at least 40 R and has a hardness value at anoperating temperature of about 350F of at least R 40.

3. An apex sea] as in claim 1, in which the asdeposited surfaceroughness of said coating is no greater than 300 r.m.s.

4. In a rotary piston engine having a rotor mounted for planetarymovement within an enclosure of said engine, the rotor carrying at leastone seal element within a slot at an apex thereof, said seal beingadapted to be urged by gas pressure within said enclosure to sealagainst the side of said slot and also against said enclosure, thecombination system comprising:

a. a coating system for said enclosure consisting of a metal bondedrefractory having a hardness of at least 40 R b. an apex sealconstruction having a supporting portion adapted to extend between saidslot and the coating system of said enclosure, said supporting portionconsisting essentially of aluminum and having a curved crown adapted tofacilitate sliding engagement with said enclosure coating system, and acontinuous wear-resistant coating having a thickness less than 0.025inch, said coating substantially enveloping said supporting portion andbeing mechanically bonded to and enveloping at least the full crown ofsaid supporting portion with an adhesive force of at least 8,500 p.s.i.as determined by an epoxy test procedure, szaid wear-resistant coatingconsisting essentially of an admixture of a metal and a refractorypowder with the particle size of said powders not exceeding 74 microns,said powders being self-fusedto each other and impacted after havingbeen subjected to a temperature in the with each other and to saidsupporting portion to range of 2,800F and impelled by a plasma jetpossess an improved matallurgical union, the coatstream having avelocity of at least Mach I.

ing being the result of self-fusion of the particles

1. AN APEX SEAL FOR A ROTARY INTERNAL COMBUSTION AND HAVING SURFACES TOBE SEALED COMPRISING: A. A SUPPORTING PORTION DEFINED TO ESTEND BETWEENSAID SURFACES AND IS COMPRISED OF A METAL CONSISTING ESSENTIALLY OFALUMINUM AND HAVING A SPECIFIC GRAVITY NO GREATER THAN 3.0 AND A MODULUSOF ELASTICITY NO LESS THAN 12 MILLION P.S.I., B. A WEAR-RESISTANTCOATING SUBSTANTIALLY ENVELOPING SAID SUPPORTING PORTION AND HAVING ATHICKNESS BETWEEN 0.015 INCHES AND 0.025 INCHES, SAID COATING BEINGCOMPRISED OF AND ADMIXTURE OF TWO DIFFERENT TYPES OF ABRASION RESISTANTPARTICLES HAVING A PARTICLE SIZE NO GREATER THAN 74 MICRONS, SAIDPARTICLES BEING SELF-FUSED TO EACH OTHER PROVIDING LIMITED POROSITY OF2-5%, SAID COATING BEING MECHANICALLY LOCKED TO SAID SUPPORTING PORTIONWITH A UNIFORM ADHESIVE FORCE NO LESS THAN 8,500 P.S.I. AS DETERMINED BYAN EPOXY TEST PROCEDURE, SAID ADHESIVE FORCE RESULTING FROM THEIMPACTION OF SAID ABRASION RESISTANT PARTICLES AGAINST SAID SUPPORTINGPORTION BY A PLASMA JET HAVING A FLOW VELOCITY IN EXCESS OF MACH
 1. 2.An apex seal as in claim 1, in which the hardness of said as-depositedcoating is at least 40 Rc and has a hardness value at an operatingtemperature of about 350*F of at least Rc
 40. 3. An apex seal as inclaim 1, in which the as-deposited surface roughness of said coating isno greater than 300 r.m.s.
 4. In a rotary piston engine having a rotormounted for planetary movement within an enclosure of said engine, therotor carrying at least one seal element within a slot at an apexthereof, said seal being adapted to be urged by gas pressure within saidenclosure to seal against the side of said slot and also against saidenclosure, the combination system comprising: a. a coating system forsaid enclosure consisting of a metal bonded refractory having a hardnessof at least 40 Rc, b. an apex seal construction having a supportingportion adapted to extend between said slot and the coating system ofsaid enclosure, said supporting portion consisting essentially ofaluminum and having a curved crown adapted to facilitate slidingengagement with said enclosure coating system, and a continuouswear-resistant coating having a thickness less than 0.025 inch, saidcoating substantially enveloping said supporting portion and beingmechanically bonded to and enveloping at least the full crown of saidsupporting portion with an adhesive force of at least 8,500 p.s.i. asdetermined by an epoxy test procedure, said wear-resistant coatingconsisting essentially of an admixture of a metal and a refractorypowder with the particle size of said powders not exceeding 74 microns,said powders being self-fused to each other and impacted with each otherand to said supporting portion to possess an improved matallurgicalunion, the coating being the result of self-fusion of the particlesafter having been subjected to a temperature in the range of 2,800*F andimpelled by a plasma jet stream having a velocity of at least Mach I.